Mounted the Center Cabin Brace this afternoon. Finding center was quite a challenge. The fiberglass is 1 13/32 thick with a cavity in the center of about 1/4 inch ( by design). To reduce pressure on the fiberglass when the fasteners are tightened, I drilled the hole 5/16 and drove in a piece of AT6-058x5/16 tubing until it it was flush with the inside and counter sunk the top of the hole for the head of the bolt. Worked just as planned. From there I clamped, drilled and then deburred aft and L/R side cabin back up strips.